The present invention relates to a dimensionally stable contact lens composition obtained by carefully controlling the formulation ingredients, the polymerization processes, and molding techniques. The polymerized product obtained is subjected to cutting and polishing operations, followed by hydration in a buffered saline solution, to provide a stable contact lens composition having uniform physical properties.
2. Description of the Prior Art
Contact lens compositions prepared from polymeric materials are known:
U.S. Pat. No. 3,220,960 discloses hydrophilic copolymers of a monoester of acrylic or methacrylic acid with a diester of acrylic or methacrylic acid having desirable optical and physiological properties. U.S. Pat. Nos. 3,408,429 and 3,496,524 disclose various aspects of contrifugal casting and manufacturing soft contact lenses using the hydrophilic copolymers described in U.S. Pat. No. 3,220,960.
U.S. Pat. No. 3,700,761 discloses compositions comprising of HEMA (hydroxy-ethyl methacrylate) or HPMA (Hydroxy-propyl methacrylate) with PVP in proportions of 20-45%, with up to 1% MA and about 0.2% EDMA. A two stage polymerization process, followed by radiation curing, cutting and hydration provides the finished contact lens.
U.S. Pat. No. 3,816,571, 3,822,196, and 3,829,329 disclose various aspects of the fabrication procedures generally described in aforementioned Pat. No. 3,700,761.
U.S. Pat. No. 3,807,398 discloses improvements in the U.S. Pat. No. 3,700,761 by careful regulation of ingredient concentrations and the addition of certain polymerization inhibitors to stabilize the HEMA. In addition, the polymeric composition is cast in a curved break away mold which eliminates the need for grinding the cast surface of the lens.